Light emission from surface-plasmon and waveguide modes excited by N atoms near a silver grating

We examine the coupling of excited N atoms, at distances d away from a silver grating, to the usually nonradiative surface-plasmon and waveguide modes of a metal-dielectricvacuum system. For d<(D-1)-124, where D is the dielectric constant of the dielectric layer and is the wavelength of light at the frequency of the excitation, only the surface-plasmon mode exists. It is directly excited by the near field of the N atoms and radiates via the grating. For d(D-1)-124, waveguide modes also exist. They also can decay radiatively via the grating. Conservation of momentum parallel to the surface to within an integer number of Bloch waves of the grating determines the angular distribution of the emitted radiation. The agreement between the experimentally measured and theoretically predicted angular distributions is excellent. The dielectric constant of condensed N2 is deduced to be D=1.510.02 at =523 nm. © 1982 The American Physical Society.